1. Field of the Invention
The invention relates to laminated cores for rotating electric machines.
2. Related Art
As shown in FIG. 10, among rotating electric machines are brushless motors 40 used as sources for driving electric products such as video tape recorders and floppy disk drives.
The brushless motor 40 is of such a type that a magnet is rotated. Such a brushless motor includes a rotor section having a rotor magnet 34, a stator section having a stator core 24 with windings 28, and a drive circuit in the form of a circuit board 31 for controlling current to be applied to the windings 28 of the stator core 24.
As shown in FIG. 10, the stator core section of this brushless motor 40 includes: a core winding assembly 29 having the stator core 24 and the windings 28, . . . , 28 wound around salient poles 23, . . . , 23; a core holder 30, made of an electrically insulating resin, for supporting the stator core 24 so that the stator core 24 can be placed on the circuit board 31 while electrically insulated; and a lead 36 relaying electric connection between the winding 28 of each phase fixed on the core holder 30 and the drive circuit on the circuit board 31. The rotor section includes: a ringlike rotor magnet 34; a rotor case 27 for securing the rotor magnet 34; and a rotating shaft 35 for supporting the rotor case 27 firmly. The rotor section and the stator section are assembled so that the rotor magnet 34 comes outside the stator core 24 and forms a gap relative to the outer circumference of the salient poles 23. The rotating shaft 35 of the rotor section is rotatably supported by a bearing holder 32 that is fixed on the stator core 24. The bearing holder 32 is inserted from the top of the stator core 24 so as to pass through a central through hole 24a of the stator core 24 and a central through hole 30a of the core holder 30 as well as a through hole 31a of the circuit board 31. The bearing holder 32 is fixed on the circuit board 31 with machine screws 33 integrally with the stator core 24 with a flange portion 32a at the base of the bearing holder fitted with a stepped portion 24b of the stator core 24.
A conventional example of the laminated core 24 as a stator core used for a rotating electric machine (a brushless motor) is disclosed in Japanese Patent Unexamined Publication No. 23048/1990. As shown in FIG. 6, this laminated core is made of a magnetic material and is formed by arranging salient poles 23 continuously on one side along the length of a beltlike plate member 26 and spirally winding the plate member 26 so as to involute or revolute.
Since such conventional laminated core 24 is formed by spirally winding the beltlike plate member 26, a difference in level equal to the thickness of the beltlike plate member 26 is produced on each of the upper and lower surfaces of the laminated core 24 as shown in FIG. 7. Such differences in level increase the constitution of the laminated core 24, making it difficult to flatten the motor. Further, since one magnetic center M1 of the laminated core 24 and the other magnetic center M2 thereof do not coincide with each other, vibration, rotational variations, and the like are caused when such laminated core 24 is used. Still further, the presence of the difference in level on the upper surface of the laminated core 24 does not keep the size of a winding space between the upper surface of the laminated core 24 and the rotor case 27 consistent, i.e., small at a left portion designated by reference numeral 25 and large at a right portion designated by reference numeral 25', both as viewed in FIG. 7. Thus, the winding had to be made in such a manner as to fit the smaller winding space 25.
Further, in the conventional example, when a grain oriented silicon steel strip is used as a material of the beltlike plate member 26, the salient poles 23 of the laminated core 24 are designed to project in a direction orthogonal to the rolling direction A of the grain oriented silicon steel strip, thereby reducing the force of converging the magnetic flux M. In other words, the grain oriented silicon steel strip is easy to magnetize in the same direction as the rolling direction A (the magnetic flux is easy to pass through in such direction).